Apparatus and method for making free standing diamond

Abstract

A mandrel for use in a diamond deposition process has surfaces with different diamond adhesion properties. According to one embodiment, a mandrel is provided and has first and second surfaces on which a diamond film is deposited, with the second surface forming a perimeter around the first surface. The first surface of the mandrel has a first diamond bonding strength which is less than a second diamond bonding strength of the second surface. In an embodiment for forming a cup-shaped diamond film, the mandrel is a titanium nitride (TiN) coated molybdenum (Mo) substrate having a stepped solid cylindrical shape with a central mesa having a side wall or flank. The side wall is etched near the top surface of the mesa to expose a molybdenum band and to form a second surface which bounds the TiN first surface. When the molybdenum band loses efficiency as a result of diamond particles remaining in the molybdenum band after a diamond deposition procedure, a second strip of the TiN coating adjacent to the first strip may be etched or machined to expose a second band of molybdenum. Other embodiments of the invention include machining the molybdenum band on the mesa top surface, machining a stepped molybdenum band, using a separate and detachable molybdenum foil or wire applied to grooves in the mandrel, and forming radial lines or patches on the surface of the mandrel.

What is claimed is:  
     
       1. An apparatus for use in making a film of free-standing diamond, comprising: 
       a mandrel suitable for use as a substrate in a diamond deposition process having first and second deposition surfaces which are tolerant of high temperature associated with diamond deposition processes, said first surface having a first diamond bonding strength and said second surface having a second diamond bonding strength greater than said first diamond bonding strength.  
     
     
       2. An apparatus according to  claim 1 , wherein: 
       said second surface forms a perimeter completely surrounding said first surface.  
     
     
       3. An apparatus according to  claim 1 , wherein: 
       said second surface comprises a plurality of radial lines on said first surface.  
     
     
       4. An apparatus according to  claim 1 , wherein: 
       said second surface comprises a plurality of patches on said first surface.  
     
     
       5. An apparatus according to  claim 1 , wherein: 
       said first surface is titanium nitride and said second surface is molybdenum.  
     
     
       6. An apparatus according to  claim 1 , wherein: 
       said mandrel is circular with a mandrel diameter and said first surface forms a circle with a diameter smaller than said mandrel diameter, and said second surface forms an annular band around said first surface.  
     
     
       7. An apparatus according to  claim 1 , wherein: 
       said mandrel is cylindrical with a side wall and a top surface having a mandrel diameter, said first surface forms a circle with a diameter smaller than said mandrel diameter, and said second surface forms a circular band around said side wall.  
     
     
       8. An apparatus according to  claim 1 , wherein: 
       said mandrel has a cylindrical base portion having a first diameter and a cylindrical mesa portion having a second diameter smaller than said first diameter.  
     
     
       9. An apparatus according to  claim 8 , wherein: 
       said mesa has a top surface and a flank, said second surface is a band forming a perimeter completely around said flank and said first surface is an area of said mesa bounded by said second surface and including said top surface of said mesa.  
     
     
       10. An apparatus according to  claim 8 , wherein: 
       said mesa has a top surface and a flank, said second surface is an annular band forming a perimeter completely around said top surface and said first surface is an area of said top surface of said mesa bounded by said second surface.  
     
     
       11. An apparatus according to  claim 8 , wherein: 
       said mesa has a top surface and a flank, said second surface is a band forming a perimeter around said top surface and said flank, and said first surface is an area of said top surface of said mesa bounded by said second surface.  
     
     
       12. An apparatus according to  claim 8 , wherein: 
       said mandrel is a molybdenum substrate which is entirely coated with titanium nitride except for at said second surface, said second surface is an exposed portion of said underlying molybdenum made by removing a strip of said titanium nitride, and said first surface is a portion of said titanium nitride bounded by said second surface.